Respectfully Quoted: A Dictionary of Quotations. 1989.
Plutarch (46?c. 120)
[Solon] being asked, namely, what city was best to live in, That city, he replied, in which those who are not wronged, no less than those who are wronged, exert themselves to punish the wrongdoers.
PLUTARCH, Plutarchs Lives, trans. Bernadotte Perrin, life of Solon, section 18, vol. 1, p. 455 (1914).